The present invention relates to an ink jet recording apparatus, and in particular, to an ink jet recording apparatus that conducts image recording by employing photo-hardening ink that is hardened by being exposed to light.
As a method for forming images even on a base material having poor ink absorbing properties, there is known a UV ink jet recording method. In general, UV-hardening ink containing therein a photoinitiator having sensitivity to ultraviolet rays is used, and the ink impacted is exposed to ultraviolet rays. In the case of this method, an expansion of a dot diameter, ink blotting between dots and ink penetration to the base material take place until the moment when the ink is hardened by ultraviolet rays and fixed, resulting in changes of image quality.
In the UV ink jet recording method described above, factors influencing greatly on image quality in particular include sensitivity of ink, a period of time up to the exposure to light and a wavelength and intensity of a ray of light. It is preferable to shorten, to the utmost, a period of time from ink jetting to exposure to light, because problems of dot diameters and blotting become conspicuous as time passes after an ink impact.
Japanese TOKKAISHO No. 60-132767 and U.S. Pat. No. 6,145,979 disclose an ink jet recording apparatus wherein a light source is arranged immediately abreast with an ink jet head so that a period of time from ink jetting to exposure to light may be shortened.
However, rays such as ultraviolet rays radiated from a radiation apparatus sometimes adversely affect on human bodies. Therefore, for using safely an ink jet recording apparatus equipped with the radiation apparatus radiating such rays, it is necessary to provide a cover so that rays radiated from the radiation apparatus may not leak out. However, if the radiation apparatus is arranged in the space surrounded by the cover, heat generated from the light source is not radiated, and temperatures in the vicinity of the light source are raised.
Conventional light sources for ultraviolet rays include those of a type of high power and high output such as a high-pressure mercury vapor lamp and a metal halide lamp, and temperatures of heat generated from them are as high as 650–900° C., and the above-mentioned tendency was especially conspicuous.
In recent years, therefore, there is proposed to use a light source for ultraviolet rays of a type of low power and low output such as a low-pressure mercury vapor lamp and a cold-cathode tube wherein temperatures of heat generated are controlled to be as low as 70–130° C. This low output type can be used for hardening ink of a cation hardening type that is of an energy accumulating type hardened by light exposure for a long time despite low illumination intensity.
However, the luminous efficiency for the low output type has a property to depend on the temperature at metal cap of a light source that conducts discharging, resulting in a problem that it is difficult to maintain an appropriate luminous efficiency for ink hardening stably.